1. Field of the Invention
The present invention relates to a toner for use in a developer developing an electrostatic latent image formed by electrophotography, electrostatic recording, electrostatic printing, etc., and to a method for manufacturing the toner. More particularly, the present invention relates to an electrophotographic toner for use in copiers, laser printers, plain paper facsimile machines, etc., and to a method for manufacturing the toner. In addition, the present invention also relates to a color toner for use in full color copiers, full color laser printers, full color facsimile machines, which use a direct or indirect electrophotographic developing method, and to a method for manufacturing the color toner.
2. Discussion of the Background
An electrostatic latent image formed on an image bearing member, for example, by electrophotography, electrostatic recording, electroprinting or the like method is developed with a developer to form a visible image (i.e., a toner image) on the image bearing member (developing process). The toner image is then transferred onto a receiving material such as receiving paper optionally via an intermediate transfer medium (transfer process). The toner image on a receiving material is then fixed on the receiving material (fixing process).
As the developer, two-component developers consisting of a carrier and a toner and one-component developers which do not include a carrier and which consists of a magnetic or non-magnetic toner are well known. In a two-component developer, the toner is frictionally charged, for example, by contacting the carrier. In a one-component developer, the toner is frictionally charged by contacting a roller supplying the toner to a developing sleeve, a blade regulating the toner to form a toner layer on the developing sleeve and/or the like member.
In order to prepare a toner image faithfully reproducing an electrostatic latent image, the charge properties of the toner have to be properly controlled. Therefore, various charge controlling agents and methods adding the charge controlling agents have been proposed. In particular, charge controlling agents are generally expensive. In addition, a charge controlling agent effectively functions when being present at a surface of a toner. Therefore, in order to reduce manufacturing costs, it is attempted to include a small amount of a charge controlling agent on a surface or in a surface portion of toner particles.
Japanese Laid-Open Patent Publications Nos. (hereinafter referred to as JOPs) 63-104064, 05-119513, 09-127720 and 11-327199 have disclosed toners in which a charge controlling agent is adhered to the surface of the toner particles to impart a charge to the toners. However, the toners are not fully charged. In addition, a problem which occurs is that the charge controlling agent tends to be easily released from the surface of the toners. Further, the proposed methods of manufacturing the toners do not provide toners having good charging ability.
Currently, methods for manufacturing a toner such as polymerization methods, other than pulverizing methods, have been investigated. Such polymerization methods are suitable for producing toners having a relatively spherical form, a small particle diameter and a narrow particle diameter distribution. The thus prepared toners, which have a relatively spherical form and a small particle diameter, have weak attraction for image bearing members such as photoreceptors and intermediate transfer media. Therefore, toner images formed by such a toner can be transferred at a high transfer rate, and high resolution images can be formed. In addition, such a toner is hardly pulverized excessively by contact with carriers and various elements such as developing blades and cleaning blades in image forming apparatus. Therefore, such a toner can maintain its particle diameter even when used for a long period of time. The quantity of a charge controlling agent present on the surface or in the surface portion of toner particles is very important factor for such toners having a relatively spherical form and a small diameter.
JOPs 04-21862 and 2000-112180 have disclosed techniques in which a toner having a proper charge quantity and a proper charging speed is prepared by controlling the quantities of a charge controlling agent present on the surface and inside of the toner particles. These techniques are inefficient.
JOP 04-21862 specifies the ratio of the particles of a charge controlling agent present on the surface of the toner. According to the surface analysis method disclosed in JOP 04-21862, the ratio of the number of the elements present on the surface of the toner can be determined. However, the ratio of the number of molecules of the charge controlling agent at the surface of the toner particles cannot be determined because the materials present on the surface of the toner particles are not known. Even if the molecular structures of the materials present on the surface of the toner are known, the ratio of the number of the molecules of the charge controlling agent at the surface of the toner particles cannot be determined. In addition, the effect of the toner form to the charge properties of the toner is not considered in JOPs 04-21862 and 2000-112180.
JOP 2000-112180 specifies the concentration of the charge controlling agent on the surface of the toner particles and the concentration thereof in the whole toner particles. However, it is not attempted to positively arrange a charge controlling agent on the surface of toner particles, and therefore, the ratio of the concentration of the charge controlling agent on the surface of the toner particles to the concentration thereof in the whole toner particles is less than 10. Therefore, the charge rising property of the toner is not satisfactory. In addition, since a charge controlling agent is included in the inside of the toner particles, the toner has an unsatisfactory fixability and transparency.
With respect to the method of adhering a charge controlling agent, which is typically expensive, on the surface of toner particles (i.e., mother toner particles), JOP 63-244056 discloses a method in which a charge controlling agent is adhered and fixed on the surface of mother toner particles utilizing an impulse force generated at a gap between a rotor (i.e., a blade rotated at a high speed) and a stator (i.e., projections fixed on the inside wall of a vessel). However, since the inside wall has projections, crosscurrent tends to be formed, and thereby problems such that the particles are excessively pulverized, or the particles are partially melted tend to occur, resulting in performance of uneven treatment.
When the mixture is treated at such a narrow gap, a large amount of heat is induced due to impulse force at the gap, and thereby the toner particles tend to be deformed and/or are excessively pulverized. Therefore a problem such that the resultant toner has an undesired average particle diameter and/or an undesired particle diameter distribution tends to occur. In addition, a problem such that a charge controlling agent is embedded into mother toner particles and the resultant toner cannot exert the desired performance. Further, in order to prevent such problems, the processability of the mixer deteriorates because processing is performed while preventing such problems, and therefore the manufacturing method is not efficient.
JOP 08-173783 discloses a mixer as shown in FIG. 8, which has a spherical vessel 101, a driving shaft 105 arranged so as to pass through the center of a circular bottom 102 of the vessel 101, a boss 103 having a cone form and provided on the driving shaft 105, and an agitating blade 104 provided on the periphery of the boss and configured to scatter mixture particles to be treated toward the inside wall of the vessel 101. However, the mixer has a drawback in that when the rotating speed of the mixture particles to be treated approaches the rotation speed of the agitating blade, the shear stress applied to the mixture particles decreases and thereby uniform mixing such that the additive is adhered on the mother toner particles while the mother toner particles and additive are separated into their primary particles cannot be performed (hereinafter this problem is referred to as a shear stress decreasing problem).
In addition, this mixer has a function of generating circling air flow upwardly along the inside wall of the vessel to circle the mixture to be treated, but the mixer does not have a function of returning the air flow downwardly. Therefore air turbulence is generated and the mixture scattered upwardly cannot be returned to the agitating blade. Namely, a self cleaning operation is not performed by the mixture and thereby a mixture deposition problem such that the mixture tends to be deposited on the inside wall of the vessel tends to occur.
Further, when mother toner particles and a charge controlling agent (and/or a fluidity imparting agent) are mixed in a mixer, the rotating shaft is heated and therefore shaft sealing air is typically applied to the shaft to prevent deposition of the mixture on the rotating shaft. Therefore the supplied air need to be discharged from the vessel. JOP 08-173783 discloses an air discharging mechanism 106 as shown in FIG. 8 which is configured to discharge air from the vessel 101 through a filer. If the filter does not has a large area, the filter is rapidly choked with the mixture particles. Thereby air cannot be fully supplied to the rotating shaft 105, resulting in deposition of the mixture particles on the rotating shaft 105. In attempting to solve this problem, the discharging mechanism 106 is large in size and is typically projected upwardly. The mixture particles moving upwardly along the inside wall of the vessel 101 are moved toward the discharging mechanism 106, resulting in adhesion of the mixture particles on the filter of the discharging mechanism 106. Therefore uniform mixing cannot be performed, and the resultant toner has a poor charge rising property. In addition, a problem in that the mixture particles adhered on the filter fall and deposit on the vessel tends to occur.
Because of these reasons, a need exists for a toner which has a relatively spherical form and a small particle diameter and which has uniform charge properties and good charge rising property so as to produce high quality images even when used for a long period of time for image forming apparatus. In addition, a need exists for a method for efficiently manufacturing such a toner without causing toner deposition problem and shearing stress decreasing problem.